This invention relates to a solid polyelectrolyte battery with solid polyelectrolyte disposed between a positive electrode active material layer and a negative electrode active material layer.
The lithium rechargeable battery has superior characteristics such as high energy density and long storage time due to little self discharge. These characteristics are utilized in power sources for watches, calculators, cameras, etc., and in backup power supplies for Integrated Circuits (IC's).
In general, the lithium battery uses a liquid electrolyte (electrolytic solution). However, prolonged use of a liquid electrolyte battery gives rise to problems of liquid leakage and loss of electrolyte through drying. These drawbacks do not exist for a lithium battery using a solid polyelectrolyte. Many electro-chemical devices from batteries to capacitors and electro-chromic displays take advantage of the characteristics of solid polyelectrolytes. Devices can be miniaturized and made lighter through the use of solid polyelectrolytes. Further, highly reliable devices with no liquid leakage can be provided using solid polyelectrolytes. For these reasons, solid polyelectrolyte research and development has become very active in recent years.
On the other hand, these superior solid polyelectrolyte characteristics not obtainable with a liquid electrolyte are offset by the difficulty in achieving good electrode contact when used in a battery. This is because solid polyelectrolyte does not flow like liquid electrolyte. Contact between the solid polyelectrolyte and an electrode affects battery performance. If good contact is not obtained, contact resistance between the solid polyelectrolyte and the electrode increases resulting in increased internal battery resistance. Further, poor solid polyelectrolyte to electrode contact restricts ion movement resulting in reduced battery capacity. Consequently, it is extremely important that the solid polyelectrolyte is in sufficient intimate contact with electrode active material layers in a battery using a solid polyelectrolyte.
To achieve this, the use of a positive electrode composite with solid polyelectrolyte added to the positive electrode active material is cited in Japanese Non-examined Patent Publication No. 2-40867 issued Feb. 9, 1990. In the battery cited in this disclosure, electrical contact between the solid polyelectrolyte and the positive electrode active material layer is improved .by mixing a part of the solid polyelectrolyte with the positive electrode active material layer.
However, since the method cited in this disclosure layers solid polyelectrolyte on a positive electrode plate made with an electrode composite containing added solid polyelectrolyte, an ideal contact cannot be established between the positive electrode and the solid polyelectrolyte. In particular, when a solid polyelectrolyte layer with a rough surface is laminated onto the positive electrode active layer, poor contact results in effective reactive surface area variation from battery to battery, and a battery with sufficiently small internal resistance cannot be manufactured. Consequently, a solid polyelectrolyte battery with this construction has the drawback that maximum current cannot be increased, thereby making it difficult to increase battery capacity.
This invention was developed to eliminate these drawbacks. It is thus a primary object of the present invention to provide a solid polyelectrolyte battery and its method of manufacture wherein good electrical contact can be obtained between the solid polyelectrolyte and the positive electrode active layer. The above and further objects and features of this invention will more fully be apparent from the following detailed description with accompanying drawings.